1. Field of the Invention
This invention relates to a torsion torque detecting device for detecting torsion torques of wheel drive shafts of a vehicle, a slip detecting device, a road friction coefficient detecting device using the torsion torque detecting device, and a torsion torque detecting method.
2. Discussion of the Prior Art
There have been conventional devices of this kind disclosed, for instance, in Japanese Examined Patent Publications No. 50972/1992 and No. 62327/1992. These are a phase difference device which detects a torsion caused in a wheel drive shaft in transmitting a torque of an internal combustion engine which is a power unit for driving a vehicle, as a deviation of a torsion phase between two points of the wheel drive shaft, and a magnetostriction device for detecting a change in the magnetic property of the wheel drive shaft.
Further, there are a strain gage type device which electrically detects the torsion, wherein electric resistance value of a strain gage is changed by strain, and the like.
The magnetostriction type device detects a variation in torque as a change in magnetostriction of the wheel drive shaft, by a combination of an excitation coil and a detection coil which are provided in the vicinity of the wheel drive shaft.
The phase difference type device employs magnetostriction elements or optical reflecting elements installed at at least two portions of the wheel drive shaft and detects a rotation phase difference between different shaft positions.
In the strain gage type device a plurality of strain gages in the wheel drive shaft are fixed, and the torque is measured by constructing an electric bridge including these strain gages. The attaching of the respective gages is troublesome, and a telemeter or a slip ring is necessary for receiving electric signals.
With the conventional torsion torque detecting devices constructed as above, it is necessary to provide special devices for directly detecting the torque as in attaching strain gages, magnetostriction elements or the like to the wheel drive shaft for detecting the torsion torque, or installing coils for detecting the magnetostriction in the vicinity of the wheel drive shaft, and therefore, the installation thereof suffers various restrictions.